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Folded cascode opamp design?

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hebu

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How to decide the current bias of input stage and output stage of folded cascoded
opamp? In some text books which suggest us to use larger current for input
stage to boost gm, and use less current for output stage to increase ro.
But, I got a problem, the opamp linearity is poor in higher frequency opeartion if I do so. Then, I change the design to make the input stage and output stage have
equal current, the linearity is improved. (This might be due to slew rate issue)

So, I would like to know how to arrange the current bias in folded cascoded op
in general?
Thanks,
 

In my opinion, the best is make equal currents. Then fronts in transient will ne equal. But i can't remember any paper to conform it
 

I want to know why do you think giving equal currents for both stages is the best opinion? I have done the same for all my previous designs, but I never think about the reason!
 

Smallest current in output give bad poles at cascode, highest - too much size current sources ( transistors where summing cascode and input pair currents).
 

yxo said:
Smallest current in output give bad poles at cascode, highest - too much size current sources ( transistors where summing cascode and input pair currents).
Click to expand...


You are right. But my question is that why the optimum choice is giving the equal currents for both stages? Is it the optimum choice or only the simplest?
 

nassim_el85 said:
yxo said:
Smallest current in output give bad poles at cascode, highest - too much size current sources ( transistors where summing cascode and input pair currents).
Click to expand...


You are right. But my question is that why the optimum choice is giving the equal currents for both stages? Is it the optimum choice or only the simplest?
Click to expand...

Often simplest - is optimum choise, if design solve you problem.
 

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